Python Pandas/Matplotlib条形图颜色（按条件）

我正试图用pandas/matplotlib制作一张学生作业成绩条形图。我可以使条形图没有问题，但我想做的是选择学生分数的颜色。例如，我希望我能得到50分，你可以试试这个：

# make some arrays
score = [100, 50, 43, 67, 89, 2, 13, 56, 22, -1, 53]
homework_problem = ['A', 'B', 'C', 'B', 'A', 'D', 'D', 'A', 'C', 'D', 'B']
topic = ['F', 'G', 'H', 'G', 'H', 'F', 'H', 'G', 'G', 'F', 'H']

# put the arrays into a pandas df
df = pd.DataFrame()
df['score'] = score
df['homework_problem'] = homework_problem
df['topic'] = topic

df['scoregroup'] = pd.cut(df['score'],bins=[0,50,75,100], labels=['Poor','Bad','Good'])

#make sure it looks okay
print(df)

# let's groupby and plot
d = df.groupby(['homework_problem','scoregroup'])['topic'].size().unstack()
d.plot(kind='bar',stacked=True, title = "Test")

输出：

    score homework_problem topic scoregroup
0     100                A     F       Good
1      50                B     G       Poor
2      43                C     H       Poor
3      67                B     G        Bad
4      89                A     H       Good
5       2                D     F       Poor
6      13                D     H       Poor
7      56                A     G        Bad
8      22                C     G       Poor
9      -1                D     F        NaN
10     53                B     H        Bad

    score homework_problem topic scoregroup
0     100                A     F       Good
1      50                B     G       Poor
2      43                C     H       Poor
3      67                B     G        Bad
4      89                A     H       Good
5       2                D     F       Poor
6      13                D     H       Poor
7      56                A     G        Bad
8      22                C     G       Poor
9      -1                D     F        NaN
10     53                B     H        Bad